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RELATIONSHIPS BETWEEN ARCHITECTURAL AND STRUCTURAL FORM 27▲ 3.9 Portuguese Pavilion, Lisbon, Portugal, Alvaro Siza, 1998.The canopy drapes between two porticoes.▲ 3.10 Dulles International Airport, Washington, DC, USA,Saarinen (Eero) and Associates, 1962. Inclined piers support thecatenary slab.buttresses resist the large inwards pull from the hanging slab. Its simplicityof detailing carries through to the design of the porticoes whichare not at all expressive of their important structural roles. Their simpleorthogonality would have been compromised if the common procedureof tapering buttress walls in acknowledgement of the reduction oftheir bending moments with height had been undertaken. The piers ofthe Dulles International Airport Terminal, Washington, DC, illustrate theusual approach. Their tapering as well as their inclination express thestrain of supporting a heavy reinforced concrete roof (Fig. 3.10).The Portuguese Pavilion plaza shelter therefore consists of two forms, thecatenary and the porticoes. Both, simple and plain, exemplify synthesisof architectural and structural form. (Chapter 6 examines the noveldetail of exposed catenary tendons at a portico-to-slab junction.)Undulating waves formed by alternating masts and catenary roofs atHall 26, Hanover, also demonstrate totally integrated architectural andstructural forms (Fig. 3.11). In stark contrast to the solid concrete porticoesof the Portuguese Pavilion, the triangulated and trestle-like mastspossess architectural qualities of lightness and transparency. Within themain interior spaces the structural steel catenary members that read as‘tension bands’ support the roof and timber ceiling, or in selected areas,glazed roof panels (Fig. 3.12).Ribbed structuresRibbed structures can also become almost synonymous with enclosurewhere they generate and define architectural form, although theirskeletal character often necessitates a separate enveloping system. Ribsusually cantilever from their foundations or are propped near their